Musnad Ahmad Hadith 22993

It is narrated from Buraidah (may Allah be pleased with him) that we laid siege to Khaybar, so Siddiq Akbar (may Allah be pleased with him) took the flag, but he returned without conquering the specific and important fort. The next day, he took the flag again and set out, but even today the fort could not be conquered, and on that day, people faced much hardship and difficulty. The Holy Prophet (ﷺ) said, "Tomorrow I will give this flag to a person whom Allah and His Messenger love, and he loves Allah and His Messenger, and he will not return without achieving victory." So, all night we remained happy at the thought that tomorrow this fort would also be conquered. When morning came, after the Fajr prayer, the Holy Prophet (ﷺ) stood up and called for the flag. People were sitting in their rows. The Holy Prophet (ﷺ) called Ali (may Allah be pleased with him), who was suffering from an eye ailment. The Holy Prophet (ﷺ) applied his saliva to his eyes and handed the flag over to him, and through his hands, the fort was conquered, although I too was among those who desired it.